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Turbine Failure Identified In CSeries Engine Event

LOS ANGELES — Bombardier says a suspected problem in the low pressure turbine (LPT) led to a sudden loss of power and uncontained failure of a Pratt & Whitney PW1500G on the first CSeries CS100 test aircraft during ground runs in Mirabel, Quebec on May 29.

Pratt, however, declines to confirm the LPT as being the source of the problem and says "we are not going to discuss that level of technical detail." The engine maker adds it has "disassembled the engine and Pratt & Whitney and Bombardier have reviewed it in-depth. We understand the issue and have developed a plan with Bombardier to resume ground and flight testing."

The event, which occurred on the No.1 (left) engine, also caused damage to the airframe and led to the grounding of the CSeries test fleet. According to the Canadian Transportation Safety Board "the crew immediately shut down the engine, observed smoke, and declared an emergency." The engine was subsequently removed for inspection and the aircraft returned to Bombardier’s nearby assembly facility for repair.

Analysts at UBS Americas Equity Research, who met with Bombardier’s CEO Pierre Beaudoin, comment that "while root cause analysis is ongoing, Bombardier emphasized that the failure was unrelated to the gearbox, and also suggested that a manufacturing defect (rather than a design flaw) may have been the cause. The subject engine was known to have problems, and Bombardier had considered sending it back to Pratt prior to incident on May 29. The engine was instead repaired at Bombardier and the failure occurred during subsequent ground-testing."

Details of what caused the apparent LPT failure, and which part of the three-stage assembly was affected, remain unknown. In the PW1500G, as with all versions of the PW1000G geared turbofan family, the low-pressure spool is de-coupled from the fan by the gear system, which enables it to rotate at around twice the speed of conventional non-geared turbofans for increased efficiency. The higher rotational speed has raised questions over potential maintenance and wear-and-tear issues, but Pratt says the speeds are comparable to well-proven earlier engines such as the JT8D. The engine maker has also focused on new flange and hub designs, as well as blade, stator and outer shroud configurations to handle the running conditions. MTU is responsible for the LPT assembly as well as the first four stages of the low pressure compressor.

Discuss this Article 4

They will figure it out and fix the problems, however it shows that they may have overlooked the significance of increased rotor RPM. Other engine testing may not have revealed the problem due to more pristine conditions. This particular engine may have had a small oil leak or other disturbance that destabilized the rotation.

The geared turbofan is nothing new, the Textron Lycoming ALF 502R-5 was used in the Bae 146, the TFE 731 first flew in 1970 and is used in various business jets. What is new is the size and thrust class.

The description of the speed of the low pressure compressor in the article correct but is a bit misleading, its the speed of the fan which is decoupled from the speed of the compressor so the fan can run SLOWER.

You are correct about the fan running slower, mostly. With the gears they are able to have a large fan and run it slower than an engine with the same fan size. This avoids blade tip shocks that reduce efficiency and contribute largely to the fan noise "buzzsaw" you hear. Along with the fan running slower than a non-geared fan of same size, the geared system does allow them to run the turbine faster to extract as mcuh energy as possible without feeding those RPMs directly to the fan. In fact, to some extent they need to keep the turbine moving fast since the reduction gear is 3:1 I believe. What they need next is a clutch and shifter in the cockpit and some more gears in that gearbox.